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Ohio's Famous Fossils

July 28, 2023

by Peg Yacobucci, Professor, School of Earth, Environment, and Society, Bowling Green State University

Did you know that Ohio is famous for its fossils? The fossil record is full of fascinating animals that lived on Earth long ago. Big and small, ferocious and adorable, Ohio’s fossils tell us so much about how ancient animals lived on our ever-changing planet.

The rocks that make up Ohio – its bedrock – were deposited on Earth’s surface during the Paleozoic Era, about 252 to 539 million years ago. That’s before the first dinosaurs appeared in the early Mesozoic Era (around 230 million years ago). Most of these rocks are made of sediment deposited at the bottom of warm, shallow seas that covered parts of North America during the Paleozoic. The fossils for which Ohio is famous are therefore mostly ocean-dwellers, including corals, brachiopods, crinoids, and trilobites.

Trilobites are extinct relatives of modern lobsters and horseshoe crabs. Like them, they had a segmented body with many legs they used to walk on the sea floor. Ohio’s official state fossil is a large trilobite called Isotelus maximus. Isotelus fossils are found in the Cincinnati area, including a foot-long individual, humongous for a trilobite!

People come to Toledo from around the world seeking a charming trilobite called Eldredgeops rana. This trilobite had a head shaped like a frog’s head. In fact, its species name, rana, means frog in Latin. Unlike a frog, however, Eldredgeops had large compound eyes with many separate lenses, like a modern housefly’s eyes. Visitors to Sylvania, Ohio’s Fossil Park may be lucky enough to find fossils of Eldredgeops.

Ohio also has an official state fossil fish called Dunkleosteus terrelli, a kind of armored placoderm whose fossils have been found around Cleveland. “Dunk” was a top ocean predator during the Late Devonian Period, growing to at least 13 feet and perhaps as much as 33 feet long and biting down with more force than any other fish, fossil or modern. However, Dunk did not have teeth! Instead, it used the sharp exposed edges of its jawbones to slice through its prey.

Everyone loves dinosaurs! While dinosaurs almost certainly lived in Ohio during the Mesozoic Era, we have no preserved rocks of that age in the state, so we will likely never find a dinosaur fossil in Ohio. However, we do find other prehistoric giants here—the mammals of the Ice Age!

During the last 130,000 years, a large ice sheet spread over Ohio and then melted back, depositing sediment and eventually forming the Great Lakes. Living near the edge of the ice sheet in Ohio were many Ice Age animals, including two kinds of extinct elephants, the woolly mammoth and the mastodon. The bones, teeth, and tusks of these giants have been found in sediments throughout Ohio.

Ohio was also home to other extinct Ice Age mammals, like elephant-sized ground sloths and even a giant beaver named Castoroides ohioensis. Can you imagine meeting this bear-sized rodent during the Ice Age? Ohio’s first people, who arrived in the region about 13,000 years ago, almost certainly did! Castoroides and the other Ice Age species lived in Ohio until about 11,000 years ago, when many large mammals died out across North America.

Take a moment to think about how much Ohio has changed over Earth history. By studying Ohio’s famous fossils, we get a glimpse into these ancient lost worlds and learn how we might conserve and protect our species in the future.

Additional images of Isotelus, Eldredgeops, and Dunkleosteus online with Creative Common licenses:,_Adams_County,_Ohio,_USA%29_4.jpg,_Middle_Devonian;_quarry_in_Sylvania,_northwestern_Ohio,_USA%29_1_%2815324284186%29.jpg [Phacops = Eldredgeops rana]

Web Resources
Fossil Park, Sylvania, Ohio:

Fossils in Ohio:

Ohio’s state invertebrate fossil, Isotelus maximus:

Ohio’s state fossil fish, Dunkleosteus terrelli:

The Ice Age in Ohio: